German Patent Publication DE 33 24 165 C2 relates to a hydraulic shock absorber with two operative ends, having a pressure tube, arranged in a housing and filled with hydraulic fluid, and several fixedly set or adjustable throttle openings, which are distributed over the length of the pressure tube and are connected on one side to a pressure chamber of the pressure tube and on the other side to hollow chambers of the housing, and having piston rod seals on the ends, wherein respectively one piston is associated with the common pressure chamber of the pressure tube. The cup-shaped piston is connected in one piece with the pressure tube. The second piston moves over the throttle bores, which results in a damping effect.
The disadvantage of this construction lies in the active piston surface, which is relatively small in relation to the exterior diameter. For this reason the throttle bores must be made very narrow, which causes problems in connection with their manufacture. In addition, dirt in the damping fluid can lead to closure of the throttle bores.
International application WO 94/17317 (PCT/DE93/01260) and German Utility Model G 93 02 454.1 also relate to a hydraulic shock absorber, wherein an axially helically extending damping groove is arranged on the piston jacket of the damping piston, wherein a coaxial, endlessly extending oil outflow groove is arranged on the interior jacket face of the oil and piston chamber, which groove is completely covered by the piston in the initial position of the piston. This shock absorber has a gas pressure reservoir and rubber cuffs as the equalizer for the amount of oil. Hydraulic shock absorbers of this type are provided with a cylinder housing with a piston and with an oil outflow regulator, which regulates the oil flow from the oil and piston chamber and causes a reduction of kinetic energy acting on the piston, and with an oil outflow valve and a spring force, which pushes the piston back into its initial position. The damping groove, which extends axially on the circumferential jacket of the piston, terminates at the front face of the piston, wherein a coaxial, endlessly extending oil outflow groove is provided on the interior jacket face of the oil and piston chamber, which in the initial position of the piston is completely covered by the piston. Two damping grooves, offset by 180.o slashed. in respect to each other, extending axially and having oil flow cross sections which are different from each other, are disposed on the circumferential jacket of the piston. The exterior circumferential rim of both the front face of the piston and the piston bottom is interrupted by the damping groove terminating in the front face of the piston and the piston bottom. This known shock absorber is furthermore said to be distinguished in that one of the damping grooves is provided with a cross section which in particular narrows continuously from the front face of the piston to the piston bottom, while the other damping groove is provided with a cross section which remains the same over its entire length and is of the same depth. The cross section of the continuously narrowing damping groove is embodied as a section of a circle. An adjustable regulating valve, which is in direct engagement with the damping groove, is provided in one damping groove for regulating the oil flow. It is furthermore proposed to provide a slider, which can be adjusted perpendicularly in respect to the damping groove, with a one-sidedly coaxial slider tip, whose axial longitudinal section corresponds to the cross section of the damping groove, wherein the slider tip can be interlockingly screwed into the damping groove. The slider should be disposed, radially and axially adjustable, directly in the cylinder housing. The slider is sealed against the housing, in particular by an O-ring. The oil outflow groove is provided with a rectangular cross section. At least one oil outflow groove is provided on the interior jacket face of the oil and piston chamber directly adjacent to the piston, which terminates on the one side in the oil outflow groove and on the other side extends past the piston when it is in its initial position. Two oil outflow grooves, which are located opposite each other and extend axially, are disposed on the interior jacket face of the oil and piston chamber. These oil outflow grooves are provided with a round cross section of little radial depth. An oil reservoir formed by a body-elastic rubber cuff is provided spatially axially behind the oil and piston chamber. The rubber cuff is a coaxial symmetrical shaped body which is respectively provided with coaxial circular flanges in the area of its two front faces. With the two flanges the rubber cuff is in engagement with a groove in a bearing sleeve. A coaxially extending gas chamber is formed between the rubber cuff and the bearing sleeve. The housing on the side of the piston rod is provided with two coaxial seals located one behind the other. The seals are formed of a sealing medium support with an O-ring, which seals coaxially toward the adjoining interior housing jacket and with a seal ring, which seals coaxially toward the piston rod. A venting groove is formed between the two sealing medium supports, wherein a venting bore is provided in the wall of the housing adjacent to the venting groove. For forming an oil gap, the piston is seated, axially displaceable to some extent, on the piston rod, in particular on a pin connected in one piece with the piston rod. A sealing disk is disposed coaxially and seated between the piston bottom of the piston and the one front face of the bearing sleeve. The outer jacket face of the sealing disk is smaller by an oil gap than the diameter of the adjoining interior jacket face of the oil and piston chamber. A spring force, seated and acting in the oil and piston chamber, is provided for returning the piston into its initial position. The housing is provided with a screw thread extending in particular over the entire outer cylindrical length. A one-sided, coaxially extending cylindrical bolt for placing a seal ring is disposed on the exterior circumference of the housing in the area of the outlet of the piston rod. Two surfaces, located opposite each other, for applying a mounting tool are disposed on the exterior circumference of the housing, in particular in the area of the housing end located opposite the exit of the piston rod.
Hydraulic shock absorbers of the previously described type are constructed extraordinarily elaborate and consist of many single parts, so that the production costs are correspondingly high. The ability to reproduce the damping behavior is reduced in particular when employing a helical groove. The rubber cuff is difficult to mount, since initially its ends have to be sufficiently stretched so that it can be passed over elements of considerably larger cross section. Afterward it must be glued in properly, which is also connected with difficulties because of the special construction. Thus the production as a whole is hard to control. Since the calculation and production of the helical groove in the production piston is connected with a relatively high outlay, the exact capability of reproducing damping curves can only be partially realized. In case of warming of the oil after several hours of operation the flow-through behavior of the hydraulic fluid in the helical groove changes and with it the characteristic curve of the entire shock absorber.
European published, non-examined patent application EP 0 386 433 (90101539.6) relates to a hydraulic shock absorber with a housing embodied particularly as a cylinder, in which a high pressure chamber filled with a hydraulic medium is disposed, which can be charged by a piston which is displaceable in a housing by means of a mass movement to be damped and displaces hydraulic medium out of the high pressure chamber in the course of its damping movement, wherein a damping device is provided, which operates pressure-dependently under the influence of the pressure prevailing in the high pressure chamber in order to regulate the displacement flow. In addition to the first damping device, which operates in a pressure-dependent manner, a second damping device, which operates in a path-dependent manner under the influence of the displacement path of the piston, is provided for regulating the displacement flow. The shock absorber has a spring-loaded intermediate piston with a double seal as the oil equalizing reservoir and a throttle needle, which plunges into a conical bore. An overpressure valve is additionally represented on the damping piston.
The double seal is disadvantageous, since it must seal on the inside as well as the outside. Furthermore, the fact of a plurality of individual parts should be stressed as being disadvantageous.
German patent publication DE 33 02 790 C2 relates to a shock absorber with a hydraulic cylinder, in whose interior an adjustment piston is disposed, which is displaceable in the axial direction and separates a high pressure chamber filled with a hydraulic fluid from a low pressure chamber, and is in connection with a piston rod which extends in the axial direction, crosses one of the chambers while reducing its fill cross section and sealingly penetrates the associated cylinder front face toward the exterior. The two pressure chambers of different fill cross section are connected on the one hand by means of an interposed spring-loaded overflow valve, which is fixed on the housing in the interior of the cylinder and whose closing force can be regulated and which opens when the high pressure chamber is compressed, and on the other hand by means of a flap valve formed in the adjustment piston and arranged parallel with the overflow valve. The low pressure chamber communicates with an equalization chamber for the hydraulic fluid. A second low pressure chamber, located on the axial side of the high pressure chamber opposite the first low pressure chamber and communicating with the first low pressure chamber via a flow conduit extending mainly in the axial direction, is interposed in the connection between the overflow valve and the first low pressure chamber which is crossed by the piston rod. The overflow valve is located in the space between the high pressure chamber and the second low pressure chamber and essentially follows the high pressure chamber directly, wherein the equalization chamber is formed by one of the low pressure chambers and is always completely filled and acted upon by a spring-loaded work piston.
The structural length, the multitude of individual parts and in particular the multitude of sealing elements and, because of this, an expensive production, are disadvantageous in this design.
International application WO 86/00675 (PCT/GB85/00298) also relates to a shock absorber, wherein a pressure control valve is provided in place of throttle bores. However, pressure control valves in shock absorbers have been shown to be trouble-prone and as a rule react too slowly. It is not possible to control different damping curves with them.
European patent publication EP 0 436 461 B1 relates to a hydraulic shock absorber for the industry, which has a piston rod on which a throttle orifice is disposed and cooperates with a throttle needle with a stepped cross section which increases from the free tip to the cylindrical, attachable part. Over its entire length with which it cooperates with the throttle orifice, the throttle needle is designed conically, wherein the conicity decreases, starting at the tip. This model operates with a diaphragm pressure reservoir as the oil equalizer and with a conically stepped throttle needle. This embodiment also has a great structural length in relation to the stroke. It is difficult to maintain the throttle needle exactly in the center. When the oil warms, the damping behavior fluctuates more strongly than with covered throttle bores.